Ab initio calculations and three different applications of unimolecular rate theory for the dissociations of CCl{sub 4}, CFCl{sub 3}, CF{sub 2}Cl{sub 2}, and CF{sub 3}Cl
- Argonne National Lab., IL (United States)
- DuPont Central Research and Development Experimental Station, Wilmington, DE (United States)
Previously measured Cl dissociation rate constants for CCl{sub 4} and CFCl{sub 3} were analyzed with three different kinetics modeling calculations. The three models differ in detail but primarily are distinguished by the manner in which the high-pressure limiting rate constant is determined: model 1 involves a calibration to transport properties of the dissociated fragments, model 2 uses a Gorin model with a hindrance parameter, and model 3 requires variational transition state thoery on an ab initio reaction path where all low-frequency motion off the path is presumed to be a free rotation. All three models have two adjustable parameters: the dissociation energy E{sub 0} and the average energy transferred to the buffer gas [{Delta}]{sub down}. All three models are found to give comparable fits to the experiment and produce quite similar values for the adjustable parameters. The values for CCl{sub 4} and CFCl{sub 3} are compared to those obtained in similar studies for CF{sub 2}Cl{sub 2} and CF{sub 3}Cl. The results indicate a substantial and consistent decrease in the C-Cl bond energy with each additional chlorine substitution in the chlorofluoromethanes. Isodesmic electronic structure calculations at the MP2 level confirm this effect but find it to be a little smaller than the experimental results indicate. Extended electronic structure calculations provide heats of formation for all nine CF{sub x}F{sub y}Cl{sub z} methyl radicals. 42 refs., 4 figs., 5 tabs.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 249665
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 18 Vol. 100; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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